1. Field of the Invention
The present invention is directed to an apparatus for separating items bearing printed matter, and in particular to an apparatus for separating letters in a letter stack so that letters can be removed from the stack, one at a time, for supply to a franking apparatus such as a postage meter.
2. Description of the Prior Art
It is often necessary to separate an item from a group of items bearing printed matter, in particular letters (envelopes). Such items are often arranged on edge behind one another as in a stack, and are supplied laterally from the stack to a separating apparatus and thereafter to a subsequent apparatus, such as a postage meter machine. The items such as letters generally lie either over one another or behind one another, and can have different thicknesses, as well as an irregular sequence of the allowable sizes. The processing of letters deposited in this way is called mixed post operation.
The forces which hinder transport of the items are hard to control in such a system, since in particular the application of force onto the letter stack (such as to maintain the stack somewhat compressed) cannot be larger than the force applied by the transport means or the guides of the subsequent apparatus on the individual letter to remove it from the stack. Thus, with a different distribution of forces letters are no longer guided, but are overly compressed and get jammed in the apparatus.
As described in European Application 376 520, conveying letters standing vertically or an edge thereof has advantages over conveying letters lying flat because the letter weights operating on the stack are smaller, and thus lower forces are required to overcome the forces of friction and forces of attraction between the letters. Moreover, for the letters standing on edge exhibit a self-orientation in relation to this edge due to the force of gravity.
An apparatus for separating postal items deposited on edge behind one another as a letter stack in a receptacle area, is described, for example, in U.S. Pat. No. 4,615,519. The letter stack is pressed against a pull-off apparatus by means of spring force applied by a pushing element guided on a carrier. The pull-off apparatus has a drive roller made of rubber plates arranged spaced from one another on an axis. A part of the roller body protrudes over a guide plate that lies opposite the receptacle area, and that also lies flat on the letter-side surface of the foremost letter of a stack. The guide plate engages, in toothed fashion, into the gaps between the rubber plates. There is an approximately constant pressure between the letter stack and the drive roller, due to the spring force. It is problematic, however, to introduce a force between the drive roller and the foremost letter that overcomes the adhesion between this letter and the letter stack, as well as between the letter and the guide plate, especially since the adhesive force can exhibit very large letter-to-letter differences, due to different weights and adhesive properties of surfaces, as well as the condition of the paper. If the drive roller slips, disturbances in the automatic operation result.
In the apparatus disclosed in U.S. Pat. No. 3,970,298, two toothed belts rotating vertically at a distance over one another between two rollers are used as a pull-off apparatus. The postal items, deposited on edge and unsorted in a magazine, are pressed against a manually adjustable stop plate by a spring-mounted pressure plate, this stop plate being arranged between the toothed belts for the support of the letter stack. On each belt, two pads are fastened in a displaced manner, oriented in a pair, which are made of a material with a relatively high friction coefficient. These pads serve to carry the letters along. During operation, there first ensues, by means of the first pair of pads, an application of force onto the letter stack, in order to separate the foremost letter from the stack and draw it forward in such a way that the rear edge of the letter drawn forward in the transport means comes into the area of the stop plate. As the belt continues to move, the second pair of pads in turn draws a letter forward, and at the same time the letter lying on the stop plate is gripped at its edge by the beveled side surfaces of the pads, and is pushed into the separating apparatus.
A disadvantage of this approach is that the introduction of forces via the edge of the letter can lead to bulging, creasing, breaking or jamming of the letter in the subsequent apparatus, and automatic operation is thus not ensured. Moreover, there is a risk of rapid wear of the pads.